Novel measurement and analysis system for investigation of partial discharge mechanism in SF6 Gas

An understanding of mechanism of partial discharge (PD) in SF₆ gas is critical for diagnosis of PD in electric power equipment and contributes to the optimization of the design of electric power applications. However, for complexity of PD characteristics under non-uniform electric field, the mechanism of PD in SF₆ is not comprehended enough. For this reason, we aim to reveal the PD mechanism by measuring current waveform, propagation characteristics and light emission of PD in SF₆ gas and analyzing these data. For this purpose, we have developed excellent measurement and analysis techniques. For an analysis of PD under ac voltage application, not only PD waveforms but also PD propagation property is essential. We have constructed partial discharge current pulse waveform analysis (PD-CPWA) system. This system has enabled us to observe PD current sequentially at high speed and analyze the propagation of PD current pulse statistically. By the application of PD-CPWA system to diagnosis of PD activity due to the metallic particle in SF₆, we could identify the particle type and size. On the other hand, for an analysis of PD under impulse voltage application, an ultra high-speed PD measurement by various methods is extremely important. In order to investigate the impulse PD mechanism spatially and temporally, the simultaneous measurement of current and light emission intensity waveforms, streak and still light emission images and temporal evolution of spectrum of PD light emission have been carried out. By using this synchronous ultra-high speed PD measurement system, we revealed the change of light emission from decomposition products depending on the step propagation of leader discharge.